The present invention relates to a Delay Locked Loop (DLL); and, more particularly, to a DLL circuit used in a semiconductor device and a computer system which need a clock generating device for compensating for a skew between an external clock and an internal clock.
In general, a DLL is a circuit for synchronizing an internal clock of a synchronous type of memory using clocks with an external clock without any error in a semiconductor memory device. That is, when an external clock is input and is to be used as an internal clock, there occurs a timing delay. In such a case, the DLL serves to synchronize the internal clock with the external clock by controlling the timing delay.
Korean Patent No. 10-0515071 discloses a DLL for reducing power consumption. FIG. 1 is a block diagram of a conventional DLL circuit disclosed in the above patent. The conventional DLL circuit includes a buffer 110, a delay line unit 120, a phase detector 130, a mix controller 140, and first and second signal processors 150 and 160.
The buffer 110 receives an external clock signal ext_clk, generates an input clock signal eclk activated at an edge of the external clock signal, and outputs the same to the delay line unit 120 to be discussed below.
The delay line unit 120 receives the input clock signal eclk from the buffer 110 and also receives first and second comparison signals from the first and the second signal processors 150 and 160 to be explained below. The delay line unit 120 delays the input clock signal eclk for a predetermined time, and outputs delayed clock signals to the first and the second signal processors 150 and 160, respectively.
More specifically, a first delay line 121 included in the delay line unit 120 takes the input clock signal eclk from the buffer 110, generates a first clock signal intclk1 by controlling a delay amount of the input clock signal eclk in response to the first comparison signal from the first signal processor 150 to be described below, and outputs the first clock signal intclk1 to the first signal processor 150.
In the meantime, a second delay line 122 provided in the delay line unit 120 accepts the input clock signal eclk from the buffer 110, generates a second clock signal intclk2 by controlling the delay amount of the input clock signal eclk in response to the second comparison signal from the second signal processor 160 and inverting the input clock signal eclk, and outputs the second clock signal intclk2 to the second signal processor 160.
The phase detector 130 receives inverted values of the first and the second clock signals intclk1 and intclk2 from the delay line unit 120, generates a phase detection signal notifying which of the falling edges of the first and the second clock signals intclk1 and intclk2 precedes the other, and provides the phase detection signal to the mix controller 140.
The mix controller 140 decides DLL locking or unlocking based on the first comparison signal from the first signal processor 150 and the second comparison signal from the second signal processor 160, which are not shown, outputs a weight K determined depending on the phase detection signal to the first and the second signal processors 150 and 160, and delivers an on/off signal on_off to the second signal processor 160 according to the DLL locking or unlocking. Here, the weight K includes a plurality of weight signals.
The first signal processor 150 receives the weight K and the first and the second clock signals intclk1 and intclk2, generates a first compensated clock signal iclk1 by using the weight and the clock signals; and takes the external clock signal ext_clk, generates the first comparison signal by comparing the external clock signal ext_clk with the first compensated clock signal iclk1, and outputs the first comparison signal to the delay line unit 120.
To be more specific, a first phase mixer 151 prepared in the first signal processor 150 receives the weight K from the mix controller 140, generates a first mixed clock signal int_clk having an adjusted duty by applying a value obtained by subtracting the weight K from ‘1’ to the first clock signal intclk1 and applying the weight K to the second clock signal intclk2, and outputs the first mixed clock signal int_clk to a first delay model unit 152 contained in the first signal processor 150.
The first delay model unit 152 receives the first mixed clock signal int_clk having the adjusted duty from the first phase mixer 151, compensates for a time difference between the external clock and the internal clock, generates the first compensated clock signal iclk1, and provides it to a first direct phase detector 153 included in the first signal processor 150.
The first direct phase detector 153 accepts the external clock signal ext_clk, generates the first comparison signal by comparing the external clock signal ext_clk with the first compensated clock signal iclk1 from the first delay model unit 152, and outputs the first comparison signal to the delay line unit 120.
Meanwhile, the second signal processor 160 receives the weight K, and the first and the second clock signals intclk1 and intclk2 and generates a second compensated clock signal iclk2 by using the weight and the clock signals; and receives the external clock signal ext_clk, generates the second comparison signal by comparing the external clock signal ext_clk with the second compensated clock signal iclk2, and outputs the second comparison signal to the delay line unit 120, wherein the processor 160 is activated or inactivated in response to the on/off signal.
A second phase mixer 161 provided in the second signal processor 160 receives the weight K from the mix controller 140, generates a second mixed clock signal intclk2′ having an adjusted duty by applying the weight K to the first clock signal intclk1 and applying a value obtained by subtracting the weight K from ‘1’ to the second clock signal intclk2, and outputs the second mixed clock signal intclk2′ to a second delay model unit 162 included in the second signal processor 160, wherein the second phase mixer 161 is activated or inactivated in response to the on/off signal.
The second delay model unit 162 receives the second mixed clock signal intclk2′ having the adjusted duty from the second phase mixer 161, compensates for a time difference between the external clock and the internal clock, generates the second compensated clock signal iclk2, and outputs the same to a second direct phase detector 163 provided in the second signal processor 160.
The second direct phase detector 163 accepts the external clock signal ext_clk, generates the second comparison signal by comparing the external clock signal ext_clk with the second compensated clock signal iclk2 from the second delay model unit 162, and outputs the second comparison signal to the delay line unit 120.
FIG. 2 is a timing diagram for operation of the DLL circuit shown in FIG. 1. First, upon completion of the DLL locking, phase-synchronized are not only the rising edges of the first and the second compensated clock signals iclk1 and iclk2 but also the rising edges of the first and the second clock signals intclk1 and intclk2 and those of the first and the second mixed clock signals int_clk and intclk2′. In order to continuously synchronize the rising edges of the first and the second clock signals intclk1 and intclk2, the second direct phase detector 163 is turned off and only the first direct phase detector 153 is turned on to control all of the two delay lines 121 and 122 included in the delay line unit 120, from the time when the DLL locking is established.
For example, when the rising edge of the first mixed clock signal int_clk lags that of the external clock signal ext_clk due to an external factor, the first direct phase detector 153 checks the phase relation therebetween and transmits a command of reducing the delay to the two delay lines 121 and 122. When the delay is reduced in the delay line unit 120 a bit according to the command, the rising edges of the first and the second clock signals intclk1 and intclk2 are advanced, so that the rising edge phase of the first mixed clock signal int_clk generated by mixing the first and the second clock signals intclk1 and intclk2 can be advanced.
After that, when the DLL circuit is operated, the delays of the two delay lines 121 and 122 are independently tuned based on the results of the direct phase detectors 153 and 163, and when the DLL circuit is locked, the delays of the two delay lines 121 and 122 are tuned by the first direct phase detector 153. Accordingly, the path of the second clock signal intclk2, namely, the second phase mixer 161, the second delay model unit 162 and the second direct phase detector 163 provided in the second signal processor 160 are all turned off after the DLL locking is established. This turn-off process reduces power consumption.
However, in the conventional DLL circuit which can adjust a duty cycle, if a power supply voltage VDD is changed after the DLL locking, the phases of the first and the second clock signals intclk1 and intclk2 may be changed. During the DLL locking process, since the two delay lines 121 and 122 pass through independent locking processes, the number of unit delays through which the first clock signal intclk1 passes is different from that of unit delays through which the second clock signal intclk2 passes. A delay amount of one unit delay is increased at a low VDD rather than a high VDD. Therefore, when the power supply voltage VDD is changed, the phases of the first and the second clock signals intclk1 and intclk2 may be changed. FIG. 3 is a waveform diagram in which the phase between the first and the second clock signals intclk1 and intclk2 is changed by td due to the change of the power supply voltage VDD after the DLL locking.
FIG. 4 is a diagram of output waveforms of the DLL in terms of td values when the phases of the first and the second clock signals intclk1 and intclk2 are misaligned by td due to the change of the power supply voltage VDD. It can be confirmed that the output waveforms of the DLL are changed according to the change of td, which lowers the performance of the DLL. Further, FIG. 4 shows that when td becomes tCK/2 (td =3.75 ns), the output of the DLL is not toggled at all.
In order to solve the foregoing problem, the path of the second clock signal intclk2, namely, the second phase mixer 161, the second delay model unit 162 and the second direct phase detector 163 provided in the second signal processor 160, may be turned on after the DLL locking. This, however, increases current consumption.